Generally, the most commonly encountered fluorescent lamps are the so called "preheat" and "rapid-start" types of fluorescent lamp. In the "preheat" type of lamp, heater current flows through the lamp electrode during lamp ignition. Thereafter, an external voltage sensitive starter opens the electrical circuit to the lamp electrodes and heater current flow is discontinued. The "rapid-start" type of fluorescent lamp normally has a constant flow of heater current through each electrode not only during ignition but also during operation of the lamp. However, heater current flow during operation, as in the "rapid-start" lamp, is lost power which undesirably reduces the operational efficiency of the lamp.
Numerous suggestions have been made for enhancing the efficiency of "rapid-start" type fluorescent lamps. For example, U.S. Pat. Nos. 4,052,687; 4,097,779; 4,114,968; 4,156,831 and 4,171,519 which are all assigned to the Assignee of the present application, provide numerous configurations for enhanced operation of "rapid-start" type fluorescent lamps. Primarily, each provides a thermally responsive circuit breaker suitable for discontinuing heater current during operation of the fluorescent lamp.
Unfortunately, it has been found that problems still exist in spite of the enumerated advantages of the above-mentioned configurations. More specifically, it has been found that contact resistance of the electrical conductors of the circuit breaker configuration utilized in a rapid-start fluorescent lamp is a continuing but erratic area of problems. For example, the Dumet electrical conductors usually employed in such structures tend to oxidize in varying degrees during the process of sealing the glass envelopes of the circuit breaker structures. Thus, oxides on the electrical conductors not only inhibit good electrical contact between the conductor and the bimetal of a circuit breaker but also are deleterious to the attainment of accurate low voltage resistance measurements. In other words, good electrical contact to the electrical conductors external to the circuit breaker enclosed within a glass bottle is difficult to obtain because of the oxides developed thereon during the sealing of the glass bottle.